WESTCHESTER COUNTY, N.Y. – Are you paying too much in property taxes in Mamaroneck? The deadline for winning a reduction is almost upon you. You have to file your protest by mail, with supporting data, by Tuesday, Feb. 19.

As a guesstimate, the homes of a third of the people reading this website are over-assessed, said David Ruzow, president of Granite Real Estate Tax Consultants in Pleasantville.

Your assessment determines the amount of your taxes and appears on your tax bill. To reflect current market values, your town multiplies the old assessment by an “equalization rate,” which puts all the properties on the same current footing.

If you haven’t challenged your property taxes for 10 years or more, you should look into doing so, said Aaron Cohen, manager of AAA Property Tax Appeal in Hawthorne. Home values have dropped in most communities or sections of communities. Your assessment might be way out of whack. You should also consider a challenge if you have any evidence that the town has over-valued your home more recently.

The evidence has to be solid. That means getting an appraisal tied to the date the town used for its own valuations. Some towns use 2012 values; others use 2011 values. If you just bought your house or refinanced, check your new appraisal against the value shown on your property-tax bill.

You can also establish current value by using “comparables” — the selling prices of homes
similar to yours.

You’ll lose, however, if all you can do is show that your neighbor’s similar house carries a lower assessment than yours, Ruzow said. Maybe your neighbor is under-assessed. All that matters is the proven value of the home you occupy.

Even if your current assessment looks right, your taxes might be too high. That’s because the equalization rate includes the value of commercial real estate. When figuring your tax, most towns multiply your assessment by what’s known as the “residential assessment ratio,” which doesn’t show on your tax bill. By that measure, your house could be valued at more than you think, and more than is reasonable. To find out, do the multiplication yourself. You can get the current ratio from this website or call your town’s assessor.

New York State publishes detailed instructions on how to handle a property-tax case, including how to fill in the required forms. If it looks too complicated, you can hire an agent to plead for you. Granite Tax Consultants charges 50 percent of any tax saving you get in the first year. You pay only for your appraisal. AAA Property charges 55 percent and pays for the appraisal.

Neither firm will take a case it doesn’t think it can win. A quick five-minute call to any agent who handles property-tax challenges will tell you whether you have a chance.